NEMA FR4

NEMA FR4 is the flame-retardant glass-cloth epoxy laminate — woven E-glass fabric bonded with brominated (or phosphorus-based halogen-free) epoxy resin, achieving UL94 V-0 flame retardancy, and defined by NEMA LI 1 as the standard flame-retardant upgrade from G10.

Two FR4 pages exist on this site. This page covers the NEMA FR4 specification — what NEMA LI 1 requires, how FR4 differs from G10 and G11, and what the standard tests measure. For practical buying information (sizes, stock, machining, applications), see the FR4 Material Hub.

NEMA FR4 at a Glance

Property	NEMA FR4 spec value
Parent material	FR4 material family
Reinforcement	Woven E-glass cloth
Resin	Brominated epoxy (TBBPA-based) or halogen-free FR epoxy
Flame retardant	Yes — UL94 V-0
NEMA standard	NEMA LI 1, Grade FR4
Flexural strength (flatwise, min)	55,000 psi
Dielectric strength (min, 1/8 in.)	400 V/mil
Continuous operating temp	266°F (130°C)
Tg	~130–140°C (standard); ≥150°C for high-Tg FR4
MIL spec	MIL-PRF-55110 (PCB); MIL-I-24768 (shapes)

How NEMA LI 1 Defines FR4

NEMA LI 1 Grade FR4 minimum requirements are identical to G10's mechanical and dielectric floors, plus the flame-retardancy requirement:

Flexural strength (flatwise): ≥ 55,000 psi
Flexural strength (edgewise): ≥ 45,000 psi
Tensile strength: ≥ 40,000 psi
Izod impact: ≥ 14 ft·lb/in
Dielectric strength (1/8 in., short-time): ≥ 400 V/mil
Water absorption: ≤ 0.10%
Flame retardancy: UL94 V-0 (self-extinguishing within 10 s) — the defining property absent from G10

The flame-retardant system in standard FR4 is typically TBBPA (tetrabromobisphenol A) coreacted into the epoxy backbone. Halogen-free FR4 uses phosphorus-based compounds per IEC 61249-2-21 for applications requiring reduced halogen content (ROHS, REACH considerations).

FR4 vs. G10 — The Critical Distinction

FR4 and G10 are NOT the same material. Do not conflate them.

	FR4	G10
Flame retardant	Yes — UL94 V-0	No
Brominated resin	Yes (typically)	No
Tg	~130–140°C	~130°C
NEMA designation	FR4	G10
PCB use	Yes — dominant standard	No (G10 predates PCB era)
Industrial thick-form use	Yes	Yes

The practical consequence: if you're ordering PCB substrate material or electrical insulation that must pass a flame-spread test in a UL-listed product, specify FR4. If flame retardancy is not required, G10 is the appropriate (and typically equivalent-cost) choice.

See G10 vs. FR4 Comparison for the full side-by-side.

FR4 vs. FR5 — Temperature Performance

FR5 adds high-Tg (~170°C) epoxy chemistry to FR4's flame retardancy:

	FR4	FR5
Flame retardant	Yes (V-0)	Yes (V-0)
Tg	~130–140°C	~170°C
Max service temp	266°F	285°F
Cost	Moderate	Higher

If your FR4 parts are softening or delaminating at operating temperature, FR5 is the direct upgrade path.

FR4 vs. G11 — Flame Retardancy vs. Higher Tg

G11 has a similar Tg (~170°C) to FR5 but no flame retardancy. FR4 has flame retardancy but lower Tg. These are different tradeoff choices, not equivalent materials.

Standards

NEMA LI 1 (Grade FR4) — primary US laminate specification
ASTM D709 — test methods for laminated thermosetting materials
IEC 60893 — IEC equivalent: HGW 2372.4 (glass-woven-fabric epoxy, flame-retardant)
MIL-PRF-55110 — military PCB laminate qualification standard (FR4 substrate)
IPC-4101 — PCB base materials standard; IPC-4101/21 (Tg ≥110°C FR4) and /26 (Tg ≥150°C) are the dominant PCB qualifications
UL94 V-0 — UL flammability standard; FR4 is recognized at V-0

Where to Go from Here

This spec page answers "what does NEMA FR4 mean?" For everything about buying, machining, sizing, and applications, go to the FR4 Material Hub.

Get a quote on [FR4 sheet](/line-card/thermoset-laminates-phenolics/glass-epoxy/fr4/sheet/), rod, or tube — flame-retardant grade, in stock

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